The present invention relates to a process for the extraction of paraffins from mixtures of paraffins and alkane-sulfonic acids.
More particularly, the present invention relates to a process for the extraction of paraffins from mixtures of said paraffins with alkane-sulfonic acids, sulfuric acid (H.sub.2 SO.sub.4) slightly polar alcohols and water (H.sub.2 O).
The mixtures of alkane-sulfonic acids and paraffins are obtained in particular by the process of sulfoxidation of n-paraffins, e.g., according to German Pat. No. 910,165, hereby incorporated by reference.
The above-mentioned mixtures present problems of recovery of alkane-sulfonic acids and their salts, and of paraffins, from the mixtures. The mixtures may also include an excess of sulfur dioxide SO.sub.2.
The presence of SO.sub.2 is not a difficult problem to overcome. Distillation under a moderate vacuum, or stripping with oxygen (O.sub.2) which is recycled to the sulfoxidation reactor, is enough to completely separate it from the solution.
For the separation of paraffins which are not converted into alkane-sulfonic acids by the above-mentioned sulfoxidation process, and of H.sub.2 SO.sub.4, several processes have been suggested. European Pat. No. 131,913 suggests isolating paraffin sulfonic acids or paraffin sulfonates from the aqueous mixture produced by sulfoxidation of the paraffins, by adding to the mixture alcohols having 2 or 3 carbon atoms, separating n-paraffins as the upper phase, and then adding a non-polar water-immiscible organic solvent, and separating the aqueous H.sub.2 SO.sub.4.
The product containing the possibly salified alkane-sulfonic acids is heated to the purpose of separating the solvent and the residual paraffins, and is possibly whitened with hydrogen peroxide.
The processes of the known art, including EP No. 131,913, suffer from the drawback that the separation of paraffins is very poor when the alcohol used has 2 or 3 carbon atoms. Subsequent heating must be carried out for a very long time, causing high energy consumption and danger of deteriorating the alkane-sulfonic acids or alkane-sulfonates.
It was surprisingly found that overcoming the drawbacks of the known art is possible by resorting to use of carbon dioxide CO.sub.2 in the supercritical state for extraction of paraffins.